U.S. patent application number 17/262490 was filed with the patent office on 2021-10-07 for reaction process involving capillary condensation within a microporous catalyst.
The applicant listed for this patent is Research Triangle Institute, University of the Basque Country. Invention is credited to Iker Aguirrezabal, Pedro Luis Arias, Marty Lail, Ignacio Luz Minguez, Mustapha Soukri.
Application Number | 20210309588 17/262490 |
Document ID | / |
Family ID | 1000005697073 |
Filed Date | 2021-10-07 |
United States Patent
Application |
20210309588 |
Kind Code |
A1 |
Aguirrezabal; Iker ; et
al. |
October 7, 2021 |
REACTION PROCESS INVOLVING CAPILLARY CONDENSATION WITHIN A
MICROPOROUS CATALYST
Abstract
Described herein is a catalytic reaction process including
introducing one or more gas-phase reactants into a reactor
comprising a microporous catalyst having a pore size less than or
equal to 2 nm and adjusting the temperature and/or the pressure of
the reactor such that one or more of the gas-phase reactants
condense within the micropores of the catalyst thereby causing the
catalytic reaction to take place in a liquid phase. Additionally, a
process for engineering defects on a carboxylate-based metal
organic framework (MOF) catalyst is described. The process includes
providing a carboxylate-based MOF catalyst; and heating the
carboxylate-based MOF catalyst in an inert gas atmosphere at
temperatures between about 150.degree. C. and about 900.degree.
C.
Inventors: |
Aguirrezabal; Iker;
(Research Triangle Park, NC) ; Luz Minguez; Ignacio;
(Research Triangle Park, NC) ; Soukri; Mustapha;
(Research Triangle Park, NC) ; Lail; Marty;
(Research Triangle Park, NC) ; Arias; Pedro Luis;
(Research Triangle Park, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Research Triangle Institute
University of the Basque Country |
Research Triangle Park
Lejona |
NC |
US
ES |
|
|
Family ID: |
1000005697073 |
Appl. No.: |
17/262490 |
Filed: |
July 17, 2019 |
PCT Filed: |
July 17, 2019 |
PCT NO: |
PCT/US19/42118 |
371 Date: |
January 22, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62703684 |
Jul 26, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C07C 2/32 20130101; C07C
2523/46 20130101; B01J 2231/12 20130101; C07C 2531/22 20130101;
B01J 2531/821 20130101; B01J 35/1057 20130101; B01J 31/1691
20130101 |
International
Class: |
C07C 2/32 20060101
C07C002/32; B01J 31/16 20060101 B01J031/16; B01J 35/10 20060101
B01J035/10 |
Claims
1. A catalytic reaction process comprising providing a reactor
comprising a microporous catalyst having a defined pore size
distribution with a pore diameter .ltoreq.2 nm, thereby allowing a
controlled pore-filling, introducing one or more gas-phase
reactants into the reactor, adjusting the temperature and/or the
pressure of the reactor such that one or more of the gas-phase
reactants, products or mixed reactant-products condense to form a
liquid phase fraction within the micropores of the catalyst,
wherein the liquid phase fraction in the micropores is controlled
to achieve a mixed liquid/gas phase within the micropores such that
the catalytic reaction takes place in a liquid phase.
2. The process of claim 1, wherein the reactor operates at a
temperature in a range of about -30.degree. C. to about 100.degree.
C. and at a pressure in a range of about 0.1 MPa and about 10
MPa.
3. The process of claim 1, further comprising, prior to introducing
the gas-phase reactant to the reactor, heating the microporous
catalyst in an inert gas atmosphere at a temperature between about
150.degree. C. and about 900.degree. C., wherein the microporous
catalyst comprises a carboxylate-based MOF catalyst.
4. The process of claim 3, wherein in the inert gas comprises
N.sub.2.
5. The process of claim 1, wherein the catalytic reaction comprises
C--C coupling reactions or chain-growth reactions, ethylene
epoxidation, ethylene hydrochlorination, CO hydrogenation
reactions, or CO.sub.2 hydrogenation reactions.
6. The process of claim 1, wherein reactions involve alcohols or
water as a condensing component.
7. A process for converting ethylene into its associated oligomer,
the process comprising providing a reactor comprising a microporous
catalyst having a pore size .ltoreq.2 nm, wherein the reactor
operates at a temperature between about -30.degree. C. and about
200.degree. C. and at a pressure between about 0.1 MPa and about 10
MPa introducing a gas-phase ethylene reactant into the reactor, and
adjusting the temperature and/or the pressure of the reactor such
that at least a portion of the gas-phase ethylene reactant
condenses within the micropores of the catalyst thereby causing the
catalytic reaction to take place in a liquid phase.
8. The process of claim 7, further comprising, prior to introducing
the gas-phase ethylene reactant to the reactor, heating the
microporous catalyst in an inert gas atmosphere at a temperature
between about 150.degree. C. and about 900.degree. C., wherein the
microporous catalyst comprises a carboxylate-based MOF
catalyst.
9. The process of claim 8, wherein in the inert gas comprises
N.sub.2.
10. A process for converting a C.sub.2-C.sub.4 alkene into its
associated oligomer, the process comprising providing a reactor
comprising a microporous catalyst having a pore size .ltoreq.2 nm,
wherein the reactor operates at a temperature between about
-30.degree. C. and about 200.degree. C. and at a pressure between
about 0.1 MPa and about 10 MPa introducing a gas-phase
C.sub.2-C.sub.4 alkene reactant into the reactor, and adjusting the
temperature and/or the pressure of the reactor such that at least a
portion of the gas-phase C.sub.2-C.sub.4 alkene reactant condenses
within the micropores of the catalyst thereby causing the catalytic
reaction to take place in a liquid phase.
11. The process of claim 10, further comprising, prior to
introducing the gas-phase reactant to the reactor, heating the
microporous catalyst in an inert gas atmosphere at a temperature
between about 150.degree. C. and about 900.degree. C., wherein the
microporous catalyst comprises a carboxylate-based MOF
catalyst.
12. The process of claim 11, wherein in the inert gas comprises
N.sub.2.
13. The process of any of the preceding claims, wherein the
microporous catalyst comprises a metal organic framework (MOF),
zeolites, zeotypes, covalent organic frameworks (COF), porous
organic polymers, porous molecular solids, porous carbons, or other
porous catalysts containing silica, organosilica, silicoaluminate,
aluminophosphate, titania, zirconia, and/or ceria.
14. The process of claim 13, wherein the MOF catalyst comprises
metals from alkali metals, alkali earth metals, transition metals,
rare earth metals or other metals.
15. The process of claim 13, wherein the MOF catalyst comprises Mg,
V, Cr, Mo, Zr, Hf, La, Zr, Mn, Fe, Co, Cu, Ni, Zn, Ru, Al, Ga, or
mixtures thereof.
16-17. (canceled)
18. The process of claim 10, wherein the C.sub.2-C.sub.4 alkene
comprises ethylene.
19. The process of claim 10, wherein the reactor operates at a
temperature between about 0.degree. C. and 100.degree. C.
20. The process of claim 10, wherein the reactor operates at a
pressure between about 3.0 MPa and 4.5 MPa.
21. The process of claim 10, wherein the reactor operates at a
pressure between about 3.5 MPa and 4.5 MPa.
22. The process of claim 10, wherein the C.sub.2-C.sub.4 alkene has
a saturation pressure Psat at the operating temperature, and
wherein the reactor is operated at a pressure P such that a
relative saturation pressure for the reactor is P/P.sub.sat is
>0.4.
23-52. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 62/703,684, filed on Jul. 26, 2018, the
entire content of which is incorporated herein by reference.
FIELD
[0002] The present disclosure describes a catalytic reaction
process involving capillary condensation of a gas-phase reactant
within the pores of a microporous catalyst. Also described is a
method for thermally engineering catalytically active sites on
metal organic frameworks.
BACKGROUND
[0003] Conventional catalysis reactions are performed using
gas-reactants (in fixed beds, slurries or bubbled in solvents) or
liquid-reactants (under pressurized conditions and/or using
additional solvents). Generally, solid-catalysts are used with
gas-reactants at relatively high temperatures because gas phase
reactants typically provide benefits in terms of enhanced
reactivity and diffusion. Generally, liquid-reactants provide
enhanced solvation effects and selectivity. It is desirable to have
a process that provides the benefits of both gas phase reactants
and liquid phase reactants.
[0004] Both liquid phase and gas phase catalyst-enabled reactions
are used to convert light alkenes into their associated dimers.
With regard to liquid phase reactions, solvent-enabled C--C
coupling of alkenes is ubiquitous in homogeneous catalysis. The
liquid phase reactions have stable rates with liquids interacting
with kinetically-relevant intermediates. Transition-metals (Ti, Ni,
Cr) within organometallic liquids or heterogeneous supports
selectively convert light alkenes (C.sub.2-C.sub.4) into highly
industrially-relevant dimers. With regard to gas phase reactions,
solid-catalysts experience fast deactivation rates due to
irreversible deposition of heavy oligomers at the higher reaction
temperatures than the ones used for liquid reaction systems.
[0005] It has been shown that catalyst deactivation rates can be
lowered for gas phase ethylene reactions if the reactants are
condensed in mesoporous catalysts having pores around 2 nm or
greater. See, Stabilization of active, selective, and regenerable
Ni-based dimerization catalysts by condensation of ethylene within
ordered mesopores, Journal of Catalysis 352 (2017) 505-514.
However, the mesopore catalysts required high-pressures and
sub-ambient temperatures to maintain the high-volatility reactants
as intrapore liquids. It would be advantageous to be able to
perform these types of capillary condensation reactions at
relatively lower pressures and industrially feasible
temperatures.
[0006] Moreover, most homogeneous catalysts or heterogeneous MOF
catalysts depend on co-catalysts for converting light alkenes to
their associated dimers because the co-catalysts allow the
formation of active ethyl-intermediate species. The dependence on
co-catalysts minimizes the practical use of MOF catalysts (and
other homogenous catalysts) in alkene oligomerization reactions. It
is desirable to provide a MOF catalyst that does not need an
activator or a solvent for alkene oligomerization reactions.
SUMMARY OF THE DISCLOSURE
[0007] A first aspect of the invention includes a catalytic
reaction process. The catalytic reaction process includes providing
a reactor including a microporous catalyst having a defined pore
size distribution with a pore diameter .ltoreq.2 nm, thereby
allowing a controlled pore-filling. The catalytic reaction process
also includes introducing one or more gas-phase reactants into the
reactor. The catalytic reaction process also includes adjusting the
temperature and/or the pressure of the reactor such that one or
more of the gas-phase reactants, products or mixed
reactant-products condense to form a liquid phase fraction within
the micropores of the catalyst. The liquid phase fraction in the
micropores can be controlled to achieve a mixed liquid/gas phase
within the micropores such that the catalytic reaction takes place
in a liquid phase.
[0008] Implementations of the first aspect may include one or more
of the following features. The process where the reactor operates
at a temperature in a range of about -30.degree. C. to about
200.degree. C. and at a pressure in a range of about 0.1 MPa and
about 10 MPa. The process further includes, prior to introducing
the one or more gas-phase reactants to the reactor, heating the
microporous catalyst in an inert gas atmosphere at a temperature
between about 150.degree. C. and about 900.degree. C., where the
microporous catalyst includes a carboxylate-based MOF catalyst. The
process where the catalytic reaction includes C--C coupling
reactions or chain-growth reactions, ethylene epoxidation, ethylene
hydrochlorination, CO hydrogenation reactions, or CO.sub.2
hydrogenation reactions. The process where the microporous catalyst
includes a metal organic framework (MOF), zeolites, zeotypes,
covalent organic frameworks (COF), porous organic polymers, porous
molecular solids, porous carbons, or other porous catalysts
containing silica, organosilica, silicoaluminate, aluminophosphate,
titania, zirconia, and/or ceria.
[0009] A second aspect of the invention includes a process for
converting ethylene into its associated oligomer. The process
includes providing a reactor including a microporous catalyst
having a pore size .ltoreq.2 nm, where the reactor operates at a
temperature between about -30.degree. C. and about 200.degree. C.
and at a pressure between about 0.1 MPa and about 10 MPa. The
process also includes introducing a gas-phase ethylene reactant
into the reactor. The process also includes adjusting the
temperature and/or the pressure of the reactor such that at least a
portion of the gas-phase ethylene reactant condenses within the
micropores of the catalyst thereby causing the catalytic reaction
to take place in a liquid phase.
[0010] A third aspect of the invention includes a process for
converting a C2-C4 alkene into its associated oligomer. The process
includes providing a reactor including a microporous catalyst
having a pore size .ltoreq.2 nm, where the reactor operates at a
temperature between about -30.degree. C. and about 200.degree. C.
and at a pressure between about 0.1 MPa and about 10 MPa. The
process also includes introducing one or more gas-phase C2-C4
alkene reactants into the reactor. The process also includes
adjusting the temperature and/or the pressure of the reactor such
that at least a portion of one or more gas-phase C2-C4 alkene
reactants condenses within the micropores of the catalyst thereby
causing the catalytic reaction to take place in a liquid phase.
[0011] A fourth aspect of the invention includes a process for
generating catalytically active sites on a carboxylate-based metal
organic framework (MOF) catalyst. The process includes providing a
carboxylate-based MOF catalyst. The process also includes heating
the carboxylate-based MOF catalyst in an inert gas atmosphere at a
temperature between about 150.degree. C. and about 900.degree.
C.
[0012] A fifth aspect of the invention includes a process for
engineering defects on a carboxylate-based metal organic framework
(MOF) catalyst. The process includes providing a carboxylate-based
MOF catalyst. The process also includes heating the
carboxylate-based MOF catalyst in an inert gas atmosphere at
temperatures between about 150.degree. C. and about 900.degree.
C.
BRIEF DESCRIPTION OF THE FIGURES
[0013] FIG. 1A is graph showing butene formation rates as a
function of temperature at 4.2 MPa ethylene (left) and as a
function of ethylene pressure at 50.degree. C. (right) as described
in Example 1.
[0014] FIG. 1B is a graph showing first-order deactivation
constants as a function of ethylene relative saturation pressure
within MOF.sub.L25 after a pretreatment in H.sub.2 at 150.degree.
C. as described in Example 1.
[0015] FIG. 2A is a graph showing thermo gravimetric analysis (TGA)
of thermal-engineering defects in a MOF.sub.L0 catalyst as
described in Example 2.
[0016] FIG. 2B is a graph showing detection of desorbed species
from mass-spectrometer (MS) signal during Ar-treatment at
200.degree. C. as described in Example 2.
[0017] FIG. 2C is a graph showing XRD analyses after
thermal-engineering defects in a MOF.sub.L0 catalyst as described
in Example 2.
[0018] FIG. 3A is a graph showing DRIFT spectra of
thermal-engineering of defects in MOF.sub.L0 in N.sub.2 as
described in Example 2.
[0019] FIG. 3B is a graph showing DRIFT spectra of
thermal-engineering of defects in MOF.sub.L0 in N.sub.2 and after
CO adsorption at 30.degree. C. as described in Example 2.
[0020] FIG. 4A is a graph showing the results of long-term
dimerization reaction stability tests for ligand-defects versus
thermal-engineered defects in MOFs at 50.degree. C. and 4.2 MPa
ethylene as described in Example 2.
[0021] FIG. 4B is a graph showing the Turnover Frequencies per Ru
atom as a function of measured defect sites (as quantified from TGA
analysis) as described in Example 2. Squared dots in b are shown
for long term stability test in (a).
DETAILED DESCRIPTION
[0022] Described herein is a catalytic reaction process involving
capillary condensation of a gas-phase reactant within the pores of
a microporous catalyst. The catalytic reaction process includes
providing a reactor comprising a microporous catalyst having a pore
size less than or equal to 2 nm, wherein the reactor operates at a
temperature and a pressure. Reactor operating temperature and
pressure can be selected and optimized based on a number of
considerations. A non-exclusive list of exemplary considerations
includes reactant composition, catalyst composition and structure,
reactor temperature and pressure limitations, and operating
temperature and pressure of associated processes. One or more
gas-phase reactants are introduced into the reactor, catalysts pore
size, and temperature and/or the pressure of the reactor can be
adjusted such that at least one or more of the gas-phase reactants
condenses within the micropores of the catalyst thereby causing the
catalytic reaction to take place in a liquid phase. Operating the
reactor in such a way as to condense at least one or more of the
gas-phase reactants into the liquid phase in the micropores of the
catalyst provides advantages that will be discussed in greater
detail below.
[0023] In an embodiment, the catalytic reaction process comprises
providing a reactor comprising a microporous catalyst having a
defined pore size distribution with a pore diameter .ltoreq.2 nm,
thereby allowing a controlled pore-filling. One or more gas-phase
reactants are introduced into the reactor. The temperature and/or
the pressure of the reactor are adjusted such that one or more of
the gas-phase reactants, products or mixed reactant-products
condenses to form a liquid phase fraction within the micropores of
the catalyst. The liquid phase fraction in the micropores is
controlled to achieve a mixed liquid/gas phase within the
micropores such that the catalytic reaction takes place in a liquid
phase. The temperature and pressure can be adjusted such that that
only a liquid phase is present within the micropores.
[0024] As mentioned above, the operating temperature and pressure
can be determined based on various operating considerations.
Generally, the reactor will be operated in a temperature range of
about -30.degree. C. to about 200.degree. C. and at a pressure
range of about 0.1 MPa and about 10 MPa. Higher or lower
temperatures and pressures may be used as appropriate. In
embodiments, the reactor may be operated at a temperature in a
range of about 0.degree. C. to about 150.degree. C. For example,
the reactor may be operated at about 0.degree. C., 20.degree. C.,
30.degree. C., 40.degree. C., 50.degree. C., 60.degree. C.,
70.degree. C., 80.degree. C., 90.degree. C., 100.degree. C.,
110.degree. C., or 120.degree. C. In embodiments, the reactor may
be operated at a pressure in a range of about 0.5 MPa to about 8
MPa. For example, the reactor may be operated at about 1.0 MPa, 1.5
MPa, 2.0 MPa, 2.5 MPa, 3.0 MPa, 3.5 MPa, 4.0 MPa, 4.5 MPa, 5.0 MPa,
5.5 MPa, 6.0 MPa, 6.5 MPa, 7.0 MPa, 7.5 MPa, or 8.0 MPa.
[0025] These reactions can be carried out in reactors containing
porous catalysts in various forms, such as fixed-bed or fluidized
flow reactors, or would also be applicable to batch reactors
allowing the intrapore condensation of reactants or products
[0026] In the process described herein, gas-reactants are at least
partially condensed into liquid-phase reactants within microporous
materials (under certain conditions of pressure and temperature)
having catalytically active sites disposed throughout the
micropores. The capillary catalytic condensation process provides
the kinetic benefits of both gas- and liquid-phase reaction
conditions. Exemplary benefits include, but are not limited to: 1)
enhanced reactivity and diffusion (gas-phase), 2) improved heat
dissipation in exothermic conditions compared to conventional
gas-phase conditions, and 3) stabilization of specific reaction
surface intermediates that directly affect catalyst deactivation
(liquid-phase). Exemplary reaction surface intermediates may
include desorption intermediates of bound species. Without being
bound by theory, it is believed that the capillary condensation of
reactants enables stabilization of reaction surface intermediates
that directly affect catalyst deactivation, providing long-term
catalyst stability within the microporous catalysts.
[0027] Microporous materials offer unique tunability in terms of
pore architecture and nature of catalytically active sites, which
enables tailoring active and stable microporous catalyst for
reactions performed under a capillary-condensation regime.
Microporous catalysts may comprise exemplary microporous materials,
including, but not limited to, metal organic frameworks (MOFs),
zeolites, zeotypes, covalent organic frameworks (COF), porous
organic polymers, porous molecular solids, porous carbons, as well
as other porous catalysts containing silica, organosilica,
silicoaluminate, aluminophosphate, titania, zirconia, and/or ceria.
As used herein, a metal organic framework (MOF) may refer to
compounds consisting of metal ions or clusters coordinated to
organic ligands to form one-, two- or three-dimensional structures,
with the special feature of porosity. More formally, a metal
organic framework is a coordination network with organic ligands
containing potential voids. In a preferred embodiment, the
nano-crystalline MOF has a percent porosity of greater than 10%,
preferably greater than 20%, preferably greater than 25%,
preferably greater than 30%, preferably greater than 35%,
preferably greater than 40%. MOFs are composed of two major
components: a metal ion or cluster of metal ions and an organic
molecule often termed a linker. The organic units are typically
mono-, di-, tri-, or tetravalent ligands. The choice of metal and
linker will dictate the structure and hence properties of the MOF.
For example, the metal's coordination preference influences the
size and shape of pores by dictating how many ligands can bind to
the metal and in which orientation. The metal ion or cluster of
metal ions associated with the MOF catalyst used herein may include
metals from alkali metals, alkali earth metals, transition metals,
rare earth metals or other metals. For example, the metal ion or
cluster of metal ions may include, without limitation, Mg, V, Cr,
Mo, Zr, Hf, La, Zr, Mn, Fe, Co, Cu, Ni, Zn, Ru, Al, Ga, or mixtures
thereof. In a preferred embodiment, the associated metal ion(s)
comprise Ru or Ni. The organic ligand associated with the MOF
catalyst may include organic ligands comprising polycarboxylate
ligands, azaheterocyclic ligands, or derivatives thereof. For
example, the organic ligand may include, without limitation,
terephthalate, benzene-1,3,5-tricarboxylate, 2,5-dioxibenzene
dicarboxylate, biphenyl-4,4'-dicarboxylate or derivatives
thereof.
[0028] In an exemplary embodiment, the linker of the MOF catalyst
comprises a carboxylate. In preferred embodiments, the MOF
structures used herein are microporous, having average pore sizes
ranging from 0 nm to 2 nm.
[0029] Many catalysts depend on co-catalysts for reactivity, which
minimizes their potential practical use in reactions (for example,
alkene oligomerization reactions). For example, homogeneous and
heterogeneous catalysts, including MOF catalysts, often require
large amounts of activators (up to 500 equivalents per active
metal) for assuring the formation and stabilization of alkyl-metal
active species during ethylene dimerization. In the process
described herein, an activator-free and solvent-free MOF catalyst
can be used to provide good dimerization reactivity and good
stability to products via capillary condensation at relatively mild
temperatures.
[0030] One or more of the gas-phase reactants may be partially
condensed or completely condensed within the micropores of the
catalyst. For example, the portion of condensed gas-phase reactants
may be 10 wt %, 20 wt %, 30 wt %, 40 wt %, 50 wt %, 60 wt %, 70 wt
%, 80 wt %, 90 wt %, or 100 wt %. In preferred embodiments, the
gas-phase reactants are completely or 100% condensed.
[0031] It is conventionally known that catalytically active open
metal sites (i.e., defects) can be engineered on Ru-based MOF
catalysts via controlled in-synthesis incorporation of
coordinatively deficient ligands (up to 30% in the MOF structure).
Catalysts with engineered defects have demonstrated an enhanced
reactivity for several reactions (e.g., alkene hydrogenation) while
maintaining structural stability. Thus, it is known that engineered
defects can be beneficial for catalytic purposes.
[0032] Advantageously, it has surprisingly been found that thermal
activation or treatment under an inert gas can produce
carboxylate-based MOF catalysts having a high concentration of
catalytically active metal-hydride sites. Thermal treatment of
previously synthesized MOF catalysts provides a general, elegant
and efficient method for engineering catalytically active sites
compared to in-synthesis incorporation of coordinatively deficient
ligands for the same purpose, which was previously used.
[0033] Thus, also described herein is a process for generating
catalytically active sites on a carboxylate-based metal organic
framework (MOF) catalyst. The process includes providing a
carboxylate-based MOF catalyst; and heating the carboxylate-based
MOF catalyst in an inert gas atmosphere at a temperature between
about 150.degree. C. and about 900.degree. C. The MOF catalyst may
be microporous or mesoporous. For example, the MOF catalyst may be
mesoporous, having pore sizes with an average diameterin the range
of 2-50 nm, preferably 4-45 nm, preferably 6-40 nm. The MOF
catalyst may be microporous, having pore sizes with an average
diameter in the range of 0-5.0 nm, preferably 1.0-3.0 nm,
preferably 1.0-2.0 nm.
[0034] The MOF catalyst can be heated at a temperature range
between about 150.degree. C. and about 900.degree. C. For example,
in embodiments, the temperature range may be about 100-700.degree.
C., about 150-600.degree. C., about 200-500.degree. C., about
200-400.degree. C., 200-300.degree. C. or about 300-400.degree. C.
In an exemplary embodiment, the MOF catalyst may be heated for a
time between about 30 minutes and about 2 hours. The concentration
of generated defects can be selected based on the end use of the
catalyst. For example, the concentration may be between about 2%
and about 50%. In embodiments, the concentration of defects may be
between about 2% and about 35%, between about 2% and about 30%,
between about 2% and about 25%, between about 2% and about 20%,
between about 5% and about 15%, or between about 7% and about
10%.
[0035] A carboxylate-based MOF catalyst that has thermally
engineered defects can be used in the catalytic capillary
condensation process described above. Thus, in embodiments, the
capillary condensation process described herein also includes
thermal treatment of the microporous catalyst prior to a gas-phase
reactant being introduced to the reactor. The microporous catalyst
can be heated in an inert gas atmosphere at a temperature between
about 150.degree. C. and about 900.degree. C. In an exemplary
embodiment, the microporous catalyst is a carboxylate-based MOF
catalyst and the inert gas is N.sub.2.
[0036] The microporous catalyst frameworks used in the capillary
condensation process described above can be thermally treated to
produce catalysts having catalytically active, selective and
highly-stable open metal sites. Combining the two concepts can
provide advantageous results.
[0037] In an exemplary embodiment of the capillary condensation
catalytic reaction process, C.sub.2-C.sub.4 alkene can be converted
into its associated oligomer. The process includes providing a
reactor comprising a microporous catalyst having a pore size
.ltoreq.2 nm, wherein the reactor operates at a temperature in a
range of about 0.degree. C. to about 200.degree. C. and at a
pressure in a range of about 0.1 MPa to about 10 MPa. The gas-phase
C.sub.2-C.sub.4 alkene reactant is introduced into the reactor, and
the temperature and/or the pressure of the reactor is adjusted such
that at least a portion of the gas-phase C.sub.2-C.sub.4 alkene
reactant condenses within the micropores of the catalyst thereby
causing the catalytic reaction to take place in a liquid phase. In
an embodiment, the C.sub.2-C.sub.4 alkene reactant comprises
ethylene.
[0038] It is recognized by those of skill in the art that
olefin-derived oligomers are a common catalyst deactivation source
in the chemical industry. As described above, the catalytic
capillary condensation process enables stabilization of reaction
surface intermediates that lead to catalyst deactivation. Thus, the
described method can provide long term stability within microporous
catalysts.
EXAMPLES
Example 1
[0039] The following is an example of ethylene dimerization
performed using the capillary condensation reaction method
described herein at varying temperatures and pressures.
[0040] A Ru-containing MOF catalyst with an average pore size of
1.5 nm was first treated at 200.degree. C. in N.sub.2 (to remove
labile adsorbates) and activated at 150.degree. C. in H.sub.2 to
generate Ru-hydride species. The MOF catalyst contained 25% of
defective ligand (MOF.sub.L25).
[0041] Ethylene was introduced to the reactor for the ethylene
dimerization reaction. To analyze the effect of temperature on the
reaction, the reactor operating temperature was varied, with
temperatures ranging from 50.degree. C. to 100.degree. C. Operating
pressure was held at 4.2 MPa during the variable temperature
period. To analyze the effect of pressure on the reaction, reactor
operating pressures were varied. Pressures ranged from 1.6 MPa to
4.2 MPa. Operating temperature was held steady at 50.degree. C.
during the variable pressure period.
[0042] FIG. 1A provides a graph showing butene formation rates as a
function of temperature and pressure. As shown in FIG. 1A, stable
ethylene dimerization rates were achieved at temperatures below
60.degree. C. (left side--pressure held at 4.2 MPa) or pressures
above 3.3 MPa (right side--temperature held at 50.degree. C.).
[0043] The reaction conditions and the narrow pore structure (1.5
nm) suggest that active-site stabilization may be related to
ethylene reactant condensation within the MOF micropores during the
reaction. FIG. 1B provides a graph showing first order deactivation
constants, derived from ethylene pressure changes (shown in FIG.
1A), as a function of ethylene relative saturation pressure within
the MOF catalyst. Catalyst deactivation was undetectable at
P/P.sub.sat>0.4, whereas lower relative saturation pressures
(P/P.sub.sat) lead to a continuous increase in first-order
deactivation constants as saturation pressures were decreased.
[0044] The decreasing rates-slopes as conversion decreased in FIG.
1A and the presence of an intrapore solvating environment suggests
that ethylene-liquid interacts with bound alkene desorption
intermediates before larger alkenes were formed.
[0045] Overall, the data in FIG. 1B show improved active Ru-hydride
stabilization in MOFs under liquid-ethylene reactants and gas-phase
precursors relative to reported MOF catalysts using activators and
various liquid solvents.
Example 2
[0046] An exemplary process for using a thermal mechanism to
engineer defects in MOF catalysts was performed. TGA and IR
analyses coupled to MS were used to demonstrate the process.
[0047] A Ru carboxylate-based MOF catalyst with no surface defects
was heated at increasing temperatures (from 0.degree. C. to
700.degree. C.) to determine the effects on the catalyst surface.
FIGS. 2A, 2B, and 2C are charts showing various analyses performed
during the staged heating process. FIG. 2A provides thermo
gravimetric analysis (TGA) of thermal-engineering defects in the
catalyst, which was originally defect free (MOF.sub.L0). FIG. 2B
provides a graph illustrating detection of desorbed species from
mass-spectrometer (MS) signal during Ar-treatment at 200.degree.
C., and FIG. 2C provides XRD analyses after thermal-engineering of
defects in the MOF catalyst.
[0048] An initial TGA-MS experiment suggested that a defect
mechanism involving ligand decarboxylation. Further TGA analysis at
increasing temperatures in N.sub.2 (FIG. 2a) enabled the
determination of the concentration of thermal-engineered defects
for the MOF sample from the weight loss in the equilibrium (after
1-hour holding). The catalyst showed 100% defect content at a
temperature of 700.degree. C.
[0049] The testing also showed that 7.3% of defects can be
engineered by thermal treatment in N.sub.2 at 200.degree. C. (FIG.
2a). This result shows that the MOF catalyst with
thermal-engineered defects would be active for ethylene
dimerization, unlike a counterpart MOF.sub.L0 catalyst heat treated
at 150.degree. C. in N.sub.2 (considered to contain 0%
defects).
[0050] As can be seen in FIGS. 3A and 3B, the mechanism for such
defect formation was also supported by IR data for MOF at
increasing temperatures in N.sub.2. FIGS. 3A and 3B are graphs
providing DRIFT spectra of thermal-engineering of defects in MOF in
N.sub.2 (A) and after CO adsorption at 30.degree. C. (B). An
apparent carboxylate protonation occurring at 200.degree. C., as a
new vibrational band appeared at 1,698 cm.sup.-1, attributed to
stretching of carbonyl of free carboxylic acids [v(C.dbd.O)],
suggests the partial reduction of at least one of the dimer Ru
atoms to compensate the charge over the MOF node. The reduction of
Ru.sup.3+ observed at this temperature range can also be supported
by two evidences: 1) the release of HCl identified by MS (FIG. 2B),
and 2) the disappearance of the IR signal attributed to
Ru.sup.3+--CO species observed for the material at 150.degree. C.
(FIG. 3B). The experimental results show the excellent defect
tunability provided by in-situ thermal engineering of MOF
catalysts. This ability is advantageous in view of more limited
in-synthesis ligand incorporation methods that have been used
previously.
[0051] As observed in the IR spectra of MOF with thermal-engineered
defects at 200-300.degree. C. (FIGS. 3A and 3B), the progressive
attenuation of signals for asymmetric stretching of carboxylates
[v.sub.sym(COO)] at 1,459 cm.sup.-1, as well as the previous signal
attributed to free carboxylic acids at 1,698 cm.sup.-1 (as phenyl
ring stretching signal at 1,384 cm.sup.-1 [v(C.dbd.C)] remains
constant), suggest that thermal activation above 200.degree. C.
occurs via cleavage of one of the carboxylates from the benzene
tricarboxylate ligand to CO.sub.2. This evidence is consistent with
the considerable weightloss due to the release of large amount of
CO.sub.2 (50% of defects at 300.degree. C., FIG. 2A). The
appearance of vibrational bands between 2100-1900 cm.sup.-1 (FIGS.
3A and 3B), attributed to CO and hydride adsorbed species on the Ru
dimer at temperatures above 200.degree. C., suggests their origin
from the homolytic cleavage of carboxylates (see FIG. 3A).
[0052] In-situ XRD monitoring as a function of temperature on
MOF.sub.L0 (FIG. 2C) revealed the remarkable structural stability
of the MOF crystalline structure up to 300.degree. C. under
N.sub.2. Higher temperatures led to the appearance of a broad
signal centered at 42 theta degrees that became even sharper
diffraction peaks above 400.degree. C., which is attributed to the
aggregation of partially reduced Ru dimers into larger metallic Ru
clusters, as also confirmed by XPS (This is accompanied by the
evident signs of the MOF structure collapse due to the advanced
degree of decarboxylation (up to 90%) and the attenuation of Ru--H
and Ru--CO adsorbed species (FIG. 3A).
[0053] These results reveal an advantageous and straightforward
route to create catalytically active sites from as-synthesized
inactive MOFs. The thermal treatment method enables the direct
utilization of MOF catalysts exhibiting thermal-generated
Ru-hydride species for ethylene dimerization without requiring any
H.sub.2-activation, as demonstrated later.
[0054] FIG. 4A is a graph showing long-term stability dimerization
rate data in the presence of intrapore liquid-ethylene for a Ru--H
catalyst species formed via ligand (H.sub.2-activated MOF.sub.L10)
and for a Ru--H catalyst species formed via thermal engineering of
defects (MOF.sub.L0 activated at 300.degree. C. under N.sub.2) at
50.degree. C. and 4.2 MPa ethylene.
[0055] As shown in FIG. 4A, the Ru--H formation control and MOF
structural stability of thermal-engineered defects seems to
extrapolate to the long-term stability tests of these MOF
catalysts. Such results indicated improved performance ability over
currently available Ni-MOF catalysts during dimerization reactions,
even in the presence of activators or liquid-solvents. Moreover,
the structural degradation observed in XRD for high-temperature
N.sub.2-activated samples (MOF.sub.L0 at 400.degree. C.) is
consistent with their low activity and slight deactivation during
dimerization, as these conditions lead to the partial loss of
porosity and thereby the intrapore liquid-filling (as seen for
MOF.sub.L50).
[0056] FIG. 4B shows ethylene dimerization turnover frequencies
(TOF, per Ru atom) as a function of measured defect content for
ligand-engineered (H.sub.2-activation at 150.degree. C.) versus MOF
catalysts with thermal-engineered defects (N.sub.2-activation at
300.degree. C.). Squared dots in FIG. 4B are shown for long term
stability tests in FIG. 4A. An evident maximum TOF value is
observed for both procedures, related to the highest available
Ru--H species, as determined by comparing the CO-DRIFT spectra
(FIG. 3B). Measured defect contents above 40% show a decline in
dimerization reactivity as a consequence of the structural collapse
and the consequent single Ru aggregation created by the excessive
deficiency of carboxylates linking the metal-organic crystalline
structure in MOFs.
[0057] Numerous modifications and variations of the present
disclosure are possible in view of the above teachings. It is
understood that within the scope of the appended claims, the
disclosure may be practiced otherwise than as specifically
described herein.
[0058] It should be understood that the above description is only
representative of illustrative embodiments and examples. For the
convenience of the reader, the above description has focused on a
limited number of representative examples of all possible
embodiments, examples that teach the principles of the disclosure.
The description has not attempted to exhaustively enumerate all
possible variations or even combinations of those variations
described. That alternate embodiments may not have been presented
for a specific portion of the disclosure, or that further
undescribed alternate embodiments may be available for a portion,
is not to be considered a disclaimer of those alternate
embodiments. One of ordinary skill will appreciate that many of
those undescribed embodiments, involve differences in technology
and materials rather than differences in the application of the
principles of the disclosure. Accordingly, the disclosure is not
intended to be limited to less than the scope set forth in the
following claims and equivalents.
* * * * *